1. Field of the Invention
This invention relates to anti-wetting ink jet nozzles and a method of precisely forming anti-wetting ink jet nozzles in single crystal silicon wafers or other single crystal semiconductor materials such as germanium or gallium arsenide. The method comprises a two-step process including a first step of physical sputter erosion, e.g., ion beam radiating of a front face of the ink jet nozzle to expose high index crystallographic planes around an ink jet nozzle orifice having an annular, polygonal or n-sided shape. The second step involves an anisotropic chemical etch that etches the front face of the wafer at a rate of 35 to 400 times that of the high index planes, which leaves behind a lip surrounding the orifice. The wafer subunits are then aligned in extended arrays to form, for example, page width printheads for ink jet type printers.
2. Description of Related Art
FIG. 1A shows a prior art ink jet printing device 1 having a conventional nozzle structure that includes an annular bore 3 and a front face 4 that is oriented perpendicular to the axis of the bore 3. Each bore 3 of an ink jetting device 1 is supplied with a supply of ink 2 that is intended to create characters on a recording medium (not shown). FIG. 1A shows the progression of ink 2 as it emerges from the bore 3 and eventually onto a recording medium. The formation of a droplet 5 eventually occurs at the mouth of the bore and gradually builds in size until the ink emerges from the bore and prints the desired character on the recording medium. Thermal ink jet devices of this type suffer in print quality when wetting 6 occurs on the front face 4 of the ink jet nozzle. This type of wetting creates imprecise character printing and often times smudging.
In addition, when a portion 7 of the ink 2 surrounding the orifice 3 dries in an asymmetrical manner as shown in FIG. 1B, a next forming droplet 8 is cohesively attracted to the side where the wetting is greatest and deflected in that direction as indicated by arrow 9. Prior art thermal ink jet devices use a hydrophobic front face coating to minimize front face wetting by the ink in an attempt to avoid these directionality problems.
Another solution is to minimize wetting by microfabricating a nozzle structure surrounding the orifice that minimizes front face wetting. Such a solution to the ink wetting problem is shown in prior art FIG. 2 which shows an ink jet nozzle 10 having a front face 11 perpendicular to a bore 12 forming a passage for ink 13 to be supplied from an unshown source. In addition, the nozzle 10 of FIG. 2 includes a lip portion 14 that serves to prevent wetting on the front face 11 of the nozzle. While this nozzle structure helps to eliminate wetting, it suffers because it is currently manufactured by expensive chemical or mechanical processes.
FIG. 3 shows a five-step chemical process by which a lip portion of the prior art device of FIG. 2 is formed. The first step is to provide a brass plate 15 as shown in step (a) and to drill a first cylindrical hole 16 and a second countersunk bore 17 within the brass plate 15 (step (b). In step (c), a layer of nickel 18 is applied by the "electroless" method to all surfaces of brass plate 15 of step (b) including top face 19, bottom face 20, and the surfaces of throughhole 16 and countersunk hole 17. In step (d), the bottom surface 21 of the nickel layer 18 and some of the brass, where necessary, are removed by grinding. Finally, in step (e), the surface 20' surrounding the nickel surface 18b coated onto annular bore 16 is selectively etched to produce a lip portion 14 of the nozzle.
FIGS. 4A and 4B show an alternative method for mechanically forming a lip portion on an ink jet nozzle. In this process, the object is to punch a hole using punch 22 in a nickel plate 23, the nickel plate forming the nozzle. A force F drives the punch 22 into the nickel plate 23. At the end of the process, a part of the nickel plate 23 will penetrate into a plastic strip 24. Because of the supporting action of steel plate 25 and the fluid behavior of plastic 24, a hole 26 without burrs and of the desired shape including a lip 27 is produced in the nickel plate 23.
U.S. Pat. No. 4,961,821 to Drake et al. discloses a method for forming throughholes in silicon wafers using an orientation dependent etching technique, and is incorporated herein by reference. As shown in FIGS. 9E and 9F of Drake, however, the ink jet nozzles encounter the same problems as those discussed in reference to FIGS. 1A and 1B. Moreover, the orifices of Drake do not provide for a lip portion that prevents wetting around the area surrounding the ink jetting orifice. In addition, the method for manufacturing the orifice includes an anisotropic method of etching that requires surfaces 31 and 32 to be covered with an etch resistant layer 34 in those areas where it is not desired to form a throughhole. Moreover, Drake anisotropically etches (100) crystallographic planes 35 and 36 using an additional etch resistant layer 34 to mask those portions of the wafer 30 not desired to be etched.